1. Field of the Invention
The present invention relates to an electrophoretic display device, and more particularly, to an electrophoretic display device having improved uniformity and a method of fabricating the same.
2. Discussion of the Related Art
In general, liquid crystal display (LCD) devices, plasma display panels (PDPs) and organic electro-luminescence displays (OLEDs) have been widely used for display devices. However, recently, to meet consumer's requirements rapidly diversified, various display devices has been introduced.
Particularly, properties of a light weight, thin profile, high efficiency and function for displaying full color moving images have been required in the display devices. To satisfy the properties, electrophoretic display devices, which have merits of papers and other display devices, have been suggested and researched. The electrophoretic display devices use a phenomenon that charged particles move to an anode or a cathode. The electrophoretic display devices have advantages in a contrast ratio, a response time, a full color display, costs, portability, and so on. Differently from the LCD devices, the electrophoretic display devices do not require a polarizer, a backlight unit, a liquid crystal layer, and so on. Accordingly, the electrophoretic display devices have an advantage in production costs.
FIG. 1 is a schematic view of a related art electrophoretic display device to explain a driving principle of the same. In FIG. 1, the related art electrophoretic display device 1 includes a first substrate 11, a second substrate 36 and an ink layer 57 interposed therebetween. The ink layer 57 includes capsules 63, and each capsule 63 has a plurality of white-dyed particles 59 and a plurality of black-dyed particles 61 therein. The white-dyed particles 59 and the black-dyed particles 61 are negatively and positively charged by a condensation polymerization reaction, respectively.
A plurality of pixel electrodes 28, which are connected to a plurality of thin film transistors (not shown), are formed on the first substrate 11, and each pixel electrode 28 is disposed in each pixel region (not shown). A positive voltage or a negative voltage is selectively applied to each of the pixel electrodes 28. When the capsules 63 including the white-dyed particles 59 and the black-dyed particles 61 have various sizes, a filtering process is performed to select the capsules 63 having a uniform size.
When a positive or negative voltage is applied to the ink layer 57, the white-dyed particles 59 and the black-dyed particles 61 in the capsules 63 move towards opposite polarities according to polarities of the applied voltage. Therefore, when the black-dyed particles 61 move upward, a black color is displayed. Alternatively, when the white-dyed particles 59 move upward, a white color is displayed.
FIG. 2 is a cross-sectional view of schematically illustrating an electrophoretic display device according to a related art. In FIG. 2, the related art electrophoretic display device 1 includes a first substrate 11, a second substrate 36 and an electrophoresis film 60 interposed therebetween. The electrophoresis film 60 includes first and second adhesive layers 51 and 53, a common electrode 55 and an ink layer 57. The first and second adhesive layers 51 and 53 face each other and include a transparent material. The common electrode 55 is formed of a transparent conductive material and is disposed on the second adhesive layer 53 to face the ink layer 57. The ink layer 57 is disposed between the first and second adhesive layers 51 and 53. The ink layer 57 includes a plurality of capsules 63, and each capsule 63 has a plurality of white-dyed particles 59 and a plurality black-dyed particles 61 therein. The white- and black-dyed particles 59 and 61 are negatively and positively charged by a condensation polymerization reaction, respectively.
The second substrate 36 includes a transparent material such as plastic or glass. The first substrate 11 includes an opaque material such as stainless steel. As occasion demands, the first substrate 11 may be formed of a transparent material such as plastic or glass. A color filter layer 40 is formed on an inner surface of the second substrate 36. The color filter layer 40 includes red, green and blue color filter patterns.
Gate lines (not shown) and data lines 19 are formed on the first substrate 11 in a matrix shape. The gate lines and the data lines 19 cross each other to define pixel regions P. A thin film transistor Tr is formed at each crossing portion of the gate lines and the data lines 19 in each pixel region P. The thin film transistor Tr includes a gate electrode 13, a gate insulating layer 16, a semiconductor layer 18, a source electrode 20 and a drain electrode 22. The gate electrode 13 extends from the gate line (not shown). The gate insulating layer 16 covers the gate electrode 13. The semiconductor layer 18 overlaps the gate electrode 13 and includes an active layer 18a and ohmic contact layers 18b. The source electrode 20 contacts the semiconductor layer 18 and extends from the data line 19. The drain electrode 22 is spaced apart from the source electrode 22.
A first passivation layer 25 and a second passivation layer 26 are formed on a substantially entire surface of the first substrate 11 including the thin film transistor Tr. The first passivation layer 25 and the second passivation layer 26 include a drain contact hole 27 exposing the drain electrode 22. The first passivation layer 25 is formed of an inorganic insulating material, and the second passivation layer 26 is formed of an organic insulating material.
A pixel electrode 28 is formed on the second passivation layer 26 in each pixel region P. The pixel electrode 28 is connected to the drain electrode 22 through the drain contact hole 27. The pixel electrode 28 is formed of a transparent conductive material, for example, one of indium-tin-oxide (ITO) and indium-zinc-oxide (IZO).
The first substrate 11 including the gate and data lines, the thin film transistor Tr and the pixel electrode 28 may be referred to as an array substrate.
The electrophoretic display device 1 having the above-mentioned structure uses ambient light, for example, natural light or room electric light, as a light source. The electrophoretic display device 1 can display images by inducing a position change of the white-dyed particles 59 and the black-dyed particles 61 in the capsule 63 depending on a polarity of a voltage applied to the pixel electrode 28.
In the electrophoretic display device 1, to drive the array substrate and the ink layer 57 of the electrophoresis film 60 attached thereto, a common voltage and a data voltage are applied to the common electrode 55 and the pixel electrode 28, respectively. A storage capacitor StgC is formed in each pixel region P to maintain a voltage difference between the common electrode 55 and the pixel electrode 28 until a next data voltage is applied. Here, in addition to the ink layer 57, the adhesive layer 51, which has a thickness of about 50 mm to about 60 mm, is interposed between the common electrode 55 and the pixel electrode 28, and thus the electrophoretic display device 1 needs a relatively high driving voltage. Accordingly, to keep the high driving voltage, a storage capacitor StgC having a large capacitance is requested.
FIG. 3 is a plan view showing a pixel region of an array substrate for an electrophoretic display device according to the related art. FIG. 4 is a cross-sectional view along the line IV-IV of FIG. 3.
In FIG. 3 and FIG. 4, a gate line 12 and a data line 19 cross each other to define a pixel region P. A thin film transistor Tr is formed at a crossing portion of the gate and data lines 12 and 19 as a switching element.
A common line 14 is formed parallel to the gate line 12 across the pixel region P. A first storage electrode 15 extends from the common line 14, and a size of the first storage electrode 15 corresponds to most of the pixel region P. A drain electrode 22 of the thin film transistor Tr includes an extending part therefrom, which overlaps the first storage electrode 15 and forms a storage capacitor StgC with a gate insulating layer 16 interposed therebetween. The extending part of the drain electrode 22 becomes a second storage electrode 24. Here, to form the above-mentioned storage capacitor StgC, the second storage electrode 24 has more than a half size of the pixel region P. However, this causes non-uniformity in patterns.
More particularly, the electrophoretic display device may be manufactured by using a mother glass substrate, which includes a plurality of array substrates for respective electrophoretic display devices. To reduce manufacturing processes and costs, a manufacturing method of an array substrate for a liquid crystal display device has been suggested and developed in which source and drain electrodes and a semiconductor layer are formed through one mask process. However, the electrophoretic display device has a different pixel region structure from a conventional liquid crystal display device. Therefore, in electrophoretic display device, if the source and drain electrodes 20 and 22 and the semiconductor layer 18 are formed through a mask process, there exists non-uniformity in patterns on the mother glass substrate, and process defects increase. Accordingly, in electrophoretic display device, the source and drain electrodes 20 and 22 and the semiconductor layer 18 are formed through two mask processes using different masks.
In addition, as stated above, the storage capacitor StgC includes the first storage electrode 15 connected to the common line 14 and the second storage electrode 24 extending from the drain electrode 22. The first storage electrode 15 is formed by using a mask, which includes a light-transmitting portion and a light-blocking portion, and a wet-etching process, and an occupying ratio per unit area is not important. However, when the source and drain electrodes 20 and 22 and the semiconductor layer 18 are formed through one mask process using a diffraction exposure method or a halftone exposure method, the source and drain electrodes 20 and 22 including the second storage electrode 24 are patterned by a dry-etching process using reactive gases. Therefore, an occupying ratio per unit area is important.
While the occupying ratios per unit area of a metallic material for the source and drain electrodes are uniform all over the mother glass substrate for liquid crystal display devices, the occupying ratios per unit area of a metallic material for the source and drain electrodes are not uniform in display areas and in non-display areas of the mother glass substrate for electrophoretic display devices because the electrophoretic display devices include relatively large-sized storage capacitors for high capacitances in the pixel regions.
Accordingly, in the electrophoretic display device, uniformity of the dry-etching process using reactive gases is not guaranteed, and defects increase when the source and drain electrodes 20 and 22 and the semiconductor layer 18 are formed through a mask process.